I had the same issue at around 40k miles. Just take your car to the dealer and they'll replace the front passenger seat coushion and sensor for you. There wasn't even a recall going on when it happened to me but they didn't hesitate to replace it.

I've got sport seats and still had the problem but I assume they would also cover sport seats if you're out of warranty on you 325 and you have sport instead of standard seats.

I had the standard seats in mine and had it replaced. I complained to the dealer before the recall about the same issues, and even after the recall was anounced, they still calimed it didnt exist until I got a postcard from BMW that said my car had been recalled. anyway, here is the link to the NHTSA recall listing.